1. Field of the Invention
The subject invention relates to information recording and playback, to magnetic tape recording, to magnetic tape transports, to tape tension equalization, and to improvement of head-to-tape contact with constant tape tension independently of variations in coil diameter and in tape velocity.
2. Information Disclosure Statement
The following disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56 (a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CFR 1.56 (a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments which may be subsequent in time or priority.
Magnetic tape transports are frequently used for data recording or storage, often in multiple tracks simultaneously. Especially in the field of instrumentation tape recording, but also in other areas, high precision of the tape motion and of other parameters are required to avoid time base errors and flutter. A great variety of prior proposals and systems are known, but have not been able to satisfy the needs met by the subject invention.
One approach drives the tape with as constant a speed as possible, effecting the reeling of the tape supply coil and the tape takeup coil at constant torque. However, that generally employed approach has the disadvantage that tape tension at the tape drive varies as a function of coil diameter. A constant tape tension in the region of the tape-head area is, however, a condition for unobjectionable data recording, since conditions, such as head-to-tape contact, tape elongation, synchronism and the like, vary especially in the area of multi track recording and playback heads with varying tape tension. Adverse consequences include objectionable output signal variations at the playback head due to varying head-to-tape contact, increased deviation from tape synchronism especially at the beginning and toward the end of the advanced tape, and increased static and dynamic time base errors at individual recording tracks through objectionable variations in elongation of the recording tape.
Tape transport with servocontrol of tape motion such as with the aid of mechanical sensors or pivoted equalizers, may approach constant tape advance, but only at a high technological effort. Such tape transports are primarily designed for large reel-to-reel systems, as may, for instance be seen from U.S. Pat. No. 3,140,033, by J. C. Zivny, issued July 7, 1964, for a pivoted magnetic tape tension equalizer, U.S. Pat. No. 3,667,700, by M. C. Carney et al, issued June 6, 1972 for a tape transport apparatus with loop formers in the tape path between the recording head and each reel, U.S. Pat. No. 4,030,131, by G. A. Beiter et al, issued June 14, 1977, for a slack tape loader with mechanical tension detectors operating in a tape drive servo system, and U.S. Pat. No. 4,104,685, by D. T. L. Chang, issued Aug. 1, 1978 for a tape transport having movable tension guides for controlling tape tension.
Often, such servo systems with mechanical tape sensors are too expensive or delicate and, in the case of tape cassettes, in which the tape is not accessible to mechanical sensor, not even practically realizable.
Apparently in an effort to overcome that drawback, there are some proposals to extract the tape from a tape cartridge, as may be seen from U.S. Pat. No. 3,619,513, by H. Morello et al, issued Nov. 9, 1971, for a retractable tape head structure with which the tape is applied to vacuum columns. That, of course, is also a very expensive approach requiring numerous electromechanical components.
A proposal addressed to a tape cassette environment is seen in U.S. Pat. No. 4,156,257, by S. L. Roberts, issued May 22, 1979, for a motor control circuit for a cassette tape drive unit.
That proposal records a speed signal in a control track, thereby utilizing space that could be employed for a further data track on the tape. Also, if head-to-tape contact is lost or becomes poor, operation with a recorded control signal obviously becomes impossible as well.
U.S. Pat. No. 4,051,415, by P. G. Martin, issued Sept. 27, 1977, for a web speed control systems, discloses use of a tachometer on each of the reel motors and employment of a reference source for adjusting drive power in a system which controls tape speed, rather than tension. Another speed control system is apparent from U.S. Pat. No. 4,157,488, by J. C. Allan, issued June 5, 1979, for methods and apparatus for controlling a tape drive to maintain a substantially constant linear tape velocity.
U.S. Pat. No. 4,398,227, by R. Anderson, issued Aug. 9, 1983, discloses a digital start/stop recorder for random access tape positioning, aiming for a predetermined amount of tape tension during initialization of the recorder, thereby realizing optimum startup conditions.
The proposal according to U.S. Pat. No. 4,015,799, by J. A. Koski et al, issued April 5, 1977, employs a type of system that requires a tape-driven tachometer, which militates against use of tape cassettes.
A proposal according to U.S. Pat. No. 4,347,538, by O. Klank, issued Aug. 31, 1982, provides methods and apparatus for measurement and indication of the position of a coiled material in tape form, with footage counter. U.S. Pat. No. 366,371, by S. M. d'Alayer de Costemore d'Arc et al, issued Dec. 28, 1982, discloses methods and apparatus for monitoring tape movement in tape cassettes, using tape position determination algorithms for determining absolute values of tape position as tape is driven from reel to reel using numerical constants stored in memory and periodically measured reel rotation speed ratios.
A capstanless magnetic tape transport system is disclosed in U.S. Pat. No. 4,256,996, by S. W. Brooks et al, issued Mar. 17, 1981, and proposing control of a supply motor to meter tape at a predetermined speed, rather than at constant tension and head-to-tape contact.
Accordingly, despite all of the above mentioned efforts, there persisted a need for relatively low-cost, high-precision tape drives where constant head-to-tape contact could be maintained with constant tape tension, without resort to mechanical sensors or large electromechanical apparatus, which is particularly vulnerable to vibration in land, sea and air vehicles, or in vibration testing environments.